1. Field of the Invention
The present invention relates to a change-speed control system for a utility vehicle having a stepless change-speed apparatus for speed-changing an engine output and transmitting the speed-changed output to a traveling unit and also a change-speed control linkage device for linking a displacement of an accelerator controller with operations of an engine speed governor and the stepless change-speed apparatus, so that the stepless change-speed apparatus may be operated to an acceleration side in association with an operation of the engine speed governor to the acceleration side.
2. Description of the Related Art
With such change-speed control system as described above, with an operation of the accelerator operation, both an adjustment of the engine speed and an adjustment of speed of the stepless change-speed apparatus can be made. A change-speed control system of this type is known from e.g. the Japanese Patent Application “Kokai” No.: Hei. 5-260827. With this known system, if a selector switch SW is set to a road traveling position, a vehicle speed controlling means C of a controller 15 is activated and a engine speed detecting sensor 17 detects an engine speed N. Then, an electric-powered cylinder 11 is driven and controlled in such a manner that an output of a stroke sensor 16 may agree with a characteristics calculated in advance for achieving a vehicle traveling speed in proportion with the detected engine speed N, so as to increase the engine speed. With this, the electric-powered cylinder 11 will be automatically driven so as to cause the vehicle traveling speed to vary in association with the increase in the engine speed, and the stepless change-speed apparatus 4 will be operated to the acceleration side.
However, in the case of the above construction in which the change-speed operation of the stepless change-speed apparatus is effected in operative connection or linkage with an engine speed adjusting operation, when the vehicle is started with speed increasing operation of the engine, in association with this, the stepless change-speed apparatus too will be shifted to the acceleration side. Then, if the stepless change-speed apparatus is shifted to the acceleration side by an acceleration ratio equal to or greater than the acceleration ratio of the engine speed, when the vehicle starts or travels at a low speed on an inclined or rough terrain, a relatively large driving load will be applied to the vehicle. So that, due to this driving load, the start of the vehicle can be hindered by insufficient engine power or even an engine stop may occur.